The network is said to have won the business after a final pitch against Carat. However, the final negotiations between OMD and Siemens are said to be ongoing and a formal announcement is expected to be made next week.
Siemens called the pitch in June to consolidate its media spend into a single global network. It initially shortlisted OMD, Carat, Universal McCann, MindShare and Zenith Optimedia Group, before a final pitch between OMD and Carat.
The majority of Siemens' spend is focused on European markets including the UK, France and Germany. However, last year it ran a major branding campaign for its mobile services division in the US, through Publicis.
Optimedia had previously handled the bulk of Siemens media in the UK - it spent £5 million last year. MediaCom handles media for Siemens' kitchen appliance range.
Siemens ran the review from its headquarters in Munich. The review did not include the creative account for its mobile division, which was won by McCann-Erickson a year ago.
Earlier this year, Siemens' group chairman, Rudi Lamprecht, said that the company would be implementing a new marketing strategy and pushing towards creating a global brand.
Recent activity for Siemens in the UK has included the sponsorship of the ITV gameshow Ant & Dec's Saturday Night Takeaway. This sponsorship deal was negotiated by Connexus, a subsidiary of Optimedia.
Siemens provides products and services in 190 countries, and it employs 484,000 staff across its divisions.
Colin Gottlieb, the chief executive of OMD Europe, was unavailable for comment as Campaign went to press.